Formation of a strong bond between a ferrous metal surface and an electrodeposit of silver



Patented Dec. 2, 1947 FORMATION OF A STRONG BOND BETWEEN A FERROUS METALSURFACE AND AN ELECTRODEPOSIT OF SILVER William M. Martz, Indianapolis,Ind., assignor to General Motors Corporation, Detroit, Mich., acorporation of Delaware No Drawing. Application March 6, 1943, SerialNo. 478,294

2 Claims. 1

This invention relates to a process of forming a high strength bondbetween an iron or steel surface and an electrodeposit of silver.

In the production of a silver plated steel surherent plating of silver.

copper may be dispensed with.

ed steel surface.

silver plated parts are annealed.

ous proportions.

room temperature.

F. or higher.

ties.

portions to the solution.

suitable.

of steel being cleaned.

suitable.

2 results the parts are given a cyanide dip before being silver plated.The cyanide solution may be one containing 100 grams of potassium orsodium cyanide per liter of water, although conface (such as, forexample, steel-backed silver 5 siderable variation in the concentrationof cyaplated bearings) it has been the practice to first nide may beemployed. The work may be imelectrodeposit a plating of a metal such ascopmersed or dipped in the cyanide solution for per or nickel onto thesteel and then electrodeto seconds. posit the silver onto the copper ornickel. This The steel parts are then given a strike or has beenessential in order to form a strong, ad- 10 flash of silver andthereafter silver plated for I have now found it the time necessary togive the desired thickness possible to form a high strength bonddirectly of silver plate. A suitable procedure for formbetweenelectrodeposited silver and steel when ing the strike of silver is toprovide a silver the steel surface is given a preliminary treatplatingbath composed of 1.5-2.5 grams per liter ment, so that the intermediatelayer of nickel or 15 of AgCN, and 150 grams per liter of KCN (free).The temperature of the bath is maintained on Broadly stated theinvention includes the the order of 75-90 F. The work is struck" inanodic treatment of the iron or steel surface the bath for a period of10 to seconds using with a phosphoric acid solution, and the subseacurrent density of 15 to amperes per square quent plating of the silverdirectly to the treat- 20 foot. The electrical contact must be madeprior Wetting agents of various to immersion in the solution for bestresults. kinds compatible with the phosphoric acid so- The parts areremoved and thereafter plated lution may be used with beneficial effect.Best with silver in a silver plating bath which preferresults areobtained when the parts are given a ably contains to grams per liter ofAgCN, cyanide dip prior to silver plating and when the -25 to grams perliter of KCN and 10 to 20 grams per liter of KOH. The bath may also con-The phosphoric acid may be employed in varitain any of the known silverbrighteners" such It is preferred that equal volas, carbon disulfide,ammonium thiosulfate, poumes of phosphoric acid (l-nPOi) and water be Itassium thiosulfate, etc., if so desired. The bath used and that thetreatment be carried out at is operated at a temperature of 100 to 125F.

However wide variation in The electrical contact should be made prior tothe proportions of phosphoric acid and water is the immersion of thepiece in the solution. For

permissible and the treatment y e Carried best results suitableagitation is provided and the out at from room temperature or below upto 150 current density permissible depends to a large 35 extent uponthis factor.

The cathodes preferably are of stainless steel For b t results t ilverplated part are and should present sufficient surface area so as l d i am- ,1 or reducing atmosphere t t pe e u Of high arfode fidensitemperature on th order of 400 to 1200 F. for

The Conta m y be of glass 1" rubber about /2 to 2 hours. The annealingmay be carlined material and should not expose any metal cied out in anair atmosphere if the temperature of the work is held below 900 F. but aneutral or The current densities at the anode may Vary reducingatmosphere is preferable. The work considerably, current densities onthe order of 5 should be allowed t 1 1 1 from the lto 150 amperes persquare foot or higher being 7 m temperature higljler currenfidensif'lies result: in 40 Before the steel surface is given the anodicmore rapid cleaning and 1n a brlghter fim treatment in the phosphoricacid solution it is The time of the anodic treatment is on the orderdesirable that the urfac s be cleaned as by of from 30 to 699 secondsdepending on the type means of an alkaline cleaning solution. A suitrable solution of this sort is composed as follows:

Direct current in the order of 6 or 12 volts 1s Per cent After the steelparts are thus treated they are Na3PO4 12 thoroughly washed as by theuse of warm run- NazSiOa 38 12 ning water and thereafter the silver iseleotro- NagCO; 6 oz'pergal'of H2O deposited directly onto the steel. Tosecure best 55 NaOH 44 l The temperature of the alkaline cleaning bathshould be 180 to 200 F. during operation. Current densities on the orderof 75 to 150 amperes per square foot are satisfactory. The work may beeither anode or cathode, preferably anodic. After the alkaline cleaningoperation the parts are rinsed thoroughly in warm running water.

To secure best results all of the plating and cleaning solutions must bekept well filtered and free from contaminations, especially oil or metaLlic particles from the anode or elsewhere.

I claim:

1. A process of producing a strongly bonded electrodeposit of silverdirectly onto a steel surface which includes, electrolytically cleaningthe said surface in an alkaline solution, washing said cleaned steelsurface, anodically treating said washed steel surface in a, solutioncomposed of approximately equal volumes of phosphoric acid and water forfrom 30 to 600 seconds, the acid solution being operated at atemperature from about room temperature up to 150 F. and at an anodecurrent density of 5 to 150 amperes per square foot, rinsing said anodictreated surface, then dipping said treated surface in an aqueous cyanidesolution composed of app o grams per liter of an alkali metal cyanide ofthe class consisting of sodium cyanide and potassium cyanide for aboutto 20 seconds, striking a silver plate onto said surface in a bathcomposed of 1.5-2.5 g./liter, silver cyanide, and 150 g./liter potassiumcyanide (free), the bath being maintained at a temperatur of 75-90 F., acurrent density of -50 amperes per square foot being employed and thetime being from 10 to 30 seconds, then electrodepositing a, silverplating of desired thickness in a silver plating bath maintained atIOU-125 F. and containing 130 to 150 g./liter of silver cyanide, 160 to180 g./liter of potassium cyanide (free) and 10 to g./liter of potassiumhydroxide, and thereafter annealing the silver plated steel surface at atemperature of 400 to 1200 F. for 30 to 120 minutes in a nonoxidizingatmosphere.

2. A process of producing a strongly bonded electrodeposit of silverdirectly onto a steel surface which includes, electrolytically cleaningthe said surface in an alkaline solution, washing said cleaned steelsurface, anodically treating said washed steel surface in a solutioncomposed of approximately equal volumes of phosphoric acid (B31304) andwater for from approximately 30 to 600 seconds, the acid solution beingoperated at a temperature from about room temperature up to 150 F. andat an anode current density of from 5 to 150 amperes per square foot,rinsing said anodically treated surface, then cyanide dipping saidtreated surface in an aqueous solution of an alkali metal cyanide of theclass consisting of sodium cyanide and potassium cyanide for about 10 to20 seconds, then striking a silver plate onto said surface in a silvercyanide electroplating strike solution, then electrodepositing a silverplate of desired thickness in a silver cyanide plating bath, andthereafter annealing said silver plated steel surface at a temperaturewith in the range of approximately 400 to 1200 F. for a time within theapproximate range of 30 to minutes in a non-oxidizing atmosphere.

WILLIAM M. MARTZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,104,269 Oplinger Jan. 4, 193811,916,503 Wilson July 4, 1933 2,197,653 Wilson Apr. 16, 1940 1,658,222Burns Feb. 27, 1928 2,277,664 Hull Mar. 31, 1942 1,995,766 Chester Mar.26, 1935 1,949,713 Gravel] Mar. 6, 1934 1,909,149 Hitner May 16, 1933OTHER REFERENCES Transactions of the Electrochemical Society, vol. 74(1938), pages 284 and 287-304.

Transactions of the Electrochemical Society, vol. 82 (1943), page 109(in the discussion of the paper The Adherence of Thick Silver Plate onSteel, by H. L. Crosby and L. I. Gilbertson, presented at th 82ndGeneral Meeting in Detroit, Michigan, Oct. 8, 1942) AmericanElectro-platers Society Monthly Review, vol. 29, (1942), an article byH. Strow on Metal Cleaning in Wartime, page 996.

